Illumination systems comprising a plurality of light sources and a remote phosphor arrangement are known per se. They are used, inter alia, in a luminaire for general lighting purposes, for example, for office lighting, for shop lighting or, for example, for in-home general lighting purposes. These illumination systems are also used in backlighting systems and display devices comprising backlighting systems.
A remote phosphor arrangement comprises luminescent material which absorbs part of the light emitted by a light source of the array of light sources and converts the absorbed light into light of a different color. When the luminescent material is arranged at a distance from the light source or light sources, a so called remote phosphor arrangement is obtained. Benefits when using the remote phosphor configuration are well known and include that the conversion efficiency and the life-time of the luminescent material are improved and that the range of luminescent materials to choose from is improved.
Such an illumination system is, for example, known from the patent application US 2006/0268537 in which a phosphor film that has a fluorescent characteristic is disclosed. In a specific embodiment of this US application a phosphor film is disclosed which is arranged remote from three light sources which are arranged in parallel. The phosphor material is arranged in areas in which the concentration of phosphor particles increased with a distance from the center of the light source. In general a phosphor has higher wavelength conversion efficiency and a larger number of converted light components as the irradiation light increases. Therefore, by increasing the concentration of the phosphor in a portion father away from the luminance center of the light source, a uniform color distribution can be generated.
A disadvantage of the known illumination system is that the uniformity of the illumination system may still be insufficient.